Method for making preforms

Abstract

An improvement in the preparation of fiber preforms in which binder and fibers are dispersed to contact on vacuum-supplied screens is disclosed, comprising particularly (a) selecting a particulate binder material which is solid at 25° C; (b) heating the binder material, during initial contact with the fibers, to a viscosity and for a time which is the same as or proportional to 1,000 centipoise for one second; and (c) dispersing the binder material and the fibers such that the preform exhibits a variation in the ratio of fibers and binder which correlates to a coefficient of variation which is less than or equal to about 5 percent. The resulting preform shows superior compaction and uniformity of constitution even when it is prepared in sections or in asymmetric configurations. A wide variety of binders can be used, including thermoplastic and thermoset polymers, glasses, ceramics, metals, and the like, and the binder can also be selected from multi-component systems which are reactive with one another, such as epoxy-based systems, and/or reactive with a resin impregnant which may be subsequently introduced. In an alternative embodiment the preforms can be heated and pressed to make final composite articles, with or without direct application of a molding resin.

What is claimed is: 
     
       1. A method of making a fiber preform, suitable for use in preparing a composite article, comprising the steps of: (a) selecting a thermoplastic binder material which is particulate and solid at 25° C.;   (b) concurrently depositing reinforcing fibers and the binder material onto one side of a foraminous screen having a vacuum means positioned on the opposite side thereof which maintains the fibers and binder material in position on the one side of the screen, wherein the binder material is heated and deposited by means of a flame spray device;   wherein the binder material is heated sufficiently by the flame spray device such that its viscosity on the screen reaches a predetermined minimum level and after the viscosity of the binder material has reached the predetermined minimum level, the binder material is returned to a solid state within a time period in seconds equal to the predetermined minimum level of viscosity in centipoise times 1/1000.   
     
     
       2. The method of claim 1 wherein the binder material is a thermoplastic organic polymer and the fibers are glass, graphite, carbon or high flexural modulus organic polymer fibers. 
     
     
       3. The method of claim 1 wherein the binder material is a thermoplastic epoxy resin. 
     
     
       4. The method of claim 1 wherein the fibers have a diameter from about 1 to about 1000 microns. 
     
     
       5. The method of claim 1 wherein the binder material is employed in an amount of from about 1 to about 20 parts by weight of binder material to about 100 parts by weight of fibers. 
     
     
       6. A method for making a fiber preform, suitable for use in preparing a composite article, comprising the steps of: (a) selecting a thermoplastic binder material which is particulate and solid at 25° C.;   (b) concurrently depositing reinforcing fibers and the binder material onto one side of a foraminous screen having vacuum means positioned on the opposite side thereof which maintains the fibers and binder material in position on the one side of the screen, wherein the binder material is heated and deposited by means of a flame spray device;   wherein (i) the binder material is heated sufficiently by the flame spray device such that its viscosity on the screen reaches a predetermined minimum level of less than about 1,000 centipoise, and (ii) after the viscosity of the binder material has reached the predetermined minimum level, the binder material is returned to its solid state in about t seconds wherein t equals the predetermined minimum level of viscosity in centipoise times 1/ 1000.   
     
     
       7. A method for making a fiber preform, suitable for use in preparing a composite article, comprising the steps of: (a) selecting a thermoplastic binder material which is particulate and solid at 25° C.;   (b) concurrently depositing reinforcing fibers and the binder material onto one side of a foraminous screen having a vacuum means positioned on the opposite side thereof which maintains the fibers and binder material in position on the one side of the screen, wherein the binder material is heated and deposited by means of a flame spray device;   wherein (i) the binder material is heated sufficiently by the flame spray device such that its viscosity on the screen is a predetermined minimum level of from 1,000-2,000 centipoise, and (ii) after the viscosity of the binder material has reached the predetermined minimum level, the binder material is returned to its solid state in about t seconds wherein t equals the predetermined minimum level of viscosity in centipoise times 1/1000.   
     
     
       8. A method of comprising the steps of: (a) selecting a thermoplastic binder material which is particulate and solid at 25° C.;   (b) concurrently depositing reinforcing fibers and the binder material onto one side of a foraminous screen having a vacuum means positioned on the opposite side thereof which maintains the fibers and binder material in position on the one side of the screen, wherein the binder material is heated and deposited by means of a flame spray device;   wherein the binder material is heated sufficiently by the flame spray device such that its viscosity on the screen reaches a predetermined minimum level and after the viscosity of the binder material has reached the predetermined minimum level, the binder material is returned to a solid state within a time period in seconds equal to the predetermined minimum level of viscosity in centipoise times 1/1000 to thereby form a preform; and   (c) impregnating the preform with a resin which is reactive or non-reactive with the binder material.   
     
     
       9. A method of making a composite article, comprising the steps of: (a) selecting a thermoplastic binder material which is particulate and solid at 25° C.;   (b) concurrently depositing reinforcing fibers and the binder material onto one side of a foraminous screen having a vacuum means positioned on the opposite side thereof which maintains the fibers and binder material in position on the one side of the screen, wherein the binder material is heated and deposited by means of a flame spray device;   wherein the binder material is heated sufficiently by the flame spray device such that its viscosity on the screen reaches a predetermined minimum level and after the viscosity of the binder material has reached the predetermined minimum level, the binder material is returned to its solid state within a time period in seconds equal to the predetermined minimum level of viscosity in centipoise times 1/1000 to thereby form a preform; and   (c) heating and pressing the preform to form a composite article.